EP0777976A2

EP0777976A2 - Extruded filtration material

Info

Publication number: EP0777976A2
Application number: EP97100456A
Authority: EP
Inventors: John Lawson Beven; Paul David Case; Martin Coleman; Colin Campbell Greig; Peter Rex White
Original assignee: British American Tobacco Investments Ltd; British American Tobacco Co Ltd
Current assignee: British American Tobacco Investments Ltd
Priority date: 1993-03-12
Filing date: 1994-03-08
Publication date: 1997-06-11
Also published as: GB9305066D0; SG52762A1; EP0614620B1; FI950553A0; AU693727B2; DE69419050D1; AU7530296A; GR3030983T3; HU9400747D0; EP0614620A3; CN1182556A; FI941112A; RU94007652A; ATE181214T1; CN1099242A; FI950553A; ES2132336T3; AU5770594A; HUT73577A; JPH07313871A

Abstract

An extruded filtration material which is degradable and comprises or an inorganic material having a melting point above the operating temperature, a polysaccharide expansion medium, a binder and water. These ingredients are fed to an extruder and subjected to an extrusion process which involves a pressure reduction, upon extrusion from the exit die, of up to about 70 bars so that swelling of the extrudate occurs to give a cellular structure.

When exposed to the natural weather conditions, tobacco smoke filter elements comprising such material degrade without leaving a fused amalgamation of inorganic material.

Description

This invention relates to filters and filtration material, and in particular, but not exclusively to tobacco smoke filters, and methods of producing same. This application is divided out from European Patent Application No. 94301642.8 filed on 8 March 1994.
Numerous methods of making filtration material have been proposed. One method previously proposed by the Applicant was disclosed in British Patent Specification No. 2 205 102A, wherein a particulate plastics material, a polysaccharide, optionally a binder, and water are fed to an extruder which is operated under such heat and pressure conditions that upon emergence from the extruder die, the extrudate assumes a cross-section greater than that of the exit orifice of the die. The expanded product may be fed to the garniture of a cigarette filter making machine or shredded and then gathered and formed into a cigarette filter in a garniture of a cigarette filter making machine. A disadvantage with the product obtained by following the teaching in this document was that, although the product was considerably expanded, it was not very suitable for standard filter making product because at low moisture contents the product could be friable and brittle. Thus, the use of such product on a filter tipping machine, where the filter element is rolled to interattach same to the tobacco rod, would be likely to result in the physical breakage thereof. Furthermore, it has been found that polypropylene, and other plastics materials having similar melting points, fuse with itself and/or the polysaccharide expansion medium and will not break down if left in the physical environment without leaving a fused amalgamation of plastics material.
The present invention has as an object the provision of processes for producing a filtration product which is particularly suitable for filtering tobacco smoke and which is degradable, especially under the weather conditions of the natural environment.
It is a further object of the present invention to provide a filtration product which has physical characteristics which are suitable for the manufacture of tobacco smoke filtration elements and filter tipped cigarettes, and which is degradable, especially under the weather conditions of the natural environment.
The weather conditions of the natural environment can be simulated using a Q.U.V. Weathering Tester (Horizontal Option) made by the Q - Panel Company. This machine reproduces the damage caused by sunlight, rain and dew on materials placed outdoors. As is illustrated in the parent application, inventive filters according to the invention of the parent application and control conventional filter elements of cellulose acetate and paper were tested by exposing samples for pre-determined time periods to alternating cycles of UV light and moisture, at controlled elevated temperatures. The conditions of the cycles were:

1. 8 hours UV light at 60°C.
2. 0.5 hours "rain" at room temperature.
3. 3.5 hours condensation at 50°C.

The present invention provides an extruded filtration material comprising inorganic material, a water-soluble polysaccharide expansion medium, a binder and water, wherein the filtration material is degradable, as defined below.
The term 'degradable' as used herein means that all water soluble or water dispersible components are dissolved or dispersed and the non-water soluble or non-water dispersible components do not form a fused or melted amalgamation. There is a change in physical form, the strength and shape of the extrudate being lost due to the effects of water and/or sunlight.
As used herein the term 'water-soluble' as applied to the polysaccharide expansion medium means a compound which goes into solution (fully or partially), or forms a suspension in water. The water-soluble polysaccharide medium may alternatively be defined as a water-suspendable polysaccharide medium. The medium in the final extruded product should also absorb water causing disintegration of the product structure because of the properties of the medium.
As used herein the term 'extruded' relates to any process where material is extruded through an orifice, under pressure or not, into conditions which subject the extruded material to a reduction in pressure. Suitably the reduction in pressure ranges from a 15 bar reduction to a 70 bar reduction upon exit from the orifice, although when sugar as a plasticiser is utilised, the pressure difference may be up to 170 bars. The pressure reduction may be achieved by extrusion into a vacuum.
The present invention further provides a process of making an extruded filtration material, wherein inorganic material, water-soluble polysaccharide expansion medium, binder and water are mixed together, and extruded through the exit orifice of an extruder die, the inorganic material being selected so that the melting point thereof is above the operating temperature of the extrusion process at any particular operating pressure, wherein the extruded product is cellular and is degradable, as defined above.
Preferably extrusion occurs under pressures at the extruder die above atmospheric pressure. Alternatively extrusion may occur at substantially atmospheric pressure into a vacuum, for example, injection moulding.
The present invention also provides a degradable smoking article comprising a degradable smoking material enwrapped in degradable wrapping material and a degradable filter comprising extruded filtration material enwrapped in degradable wrapping material, said filtration material comprising inorganic material, water-soluble polysaccharide expansion medium and binder, and produced in accordance with the above method.
Preferably in the extruded filtration material the inorganic filler material comprises 60-85% by weight, the polysaccharide expansion medium comprises 5-20% by weight, and the binder comprises 5-25% by weight, of dry materials fed to the extruder.
Preferably the filtration material is a tobacco smoke filtration material.
The inorganic material may suitably be mineral earth materials, such as vermiculite and alumina, or materials such as carbon, aluminium hydroxide or chalk. Materials such as Metaspheres 50, aluminosilicates, such as Garolite, and Trihyde may also be used. Garolite is a trade name of Croxton & Garry, Dorking for an inert low density filler of hollow silicate glass spheres. Metaspheres 50 is a Trade Name of Phillite Ltd. Trihyde is a Trade Name of Croxton & Garry, Dorking for alumina trihydrate Preferably the inorganic materials are of particulate form. Mixtures of these compounds may also be used.
The expansion medium is preferably starch, which may be natural starch, such as maize starch, having a higher proportion of amylopectin rather than amylose, or a starch having a higher proportion of amylose, such as, for example, Hylon (VII) (Registered Trade Mark) as sold by National Starch and Chemical Company. Rice or tapioca starch may also be used. Chemically modified starch, such as hydroxypropyl amylose sold under the Registered Trade Mark of Ecofoam, for example, may also be used, provided it is water-soluble to a sufficient degree. Chemically modified starches such as acid hydrolysed or enzyme hydrolysed starches may also be suitable. Suitably the starch is a food-grade starch. Mixtures of starches may also be used. Mixtures of expansion medium may also be used.
The binder material is preferably a cellulosic binder such as hydroxyethylcellulose, hydroxypropyl cellulose in particular, or a carboxymethyl cellulose, such as sodium carboxymethyl cellulose. Pectins and alginates or other similar water-soluble binders can also be used. Mixtures of binders may also be used.
Water may account, on a weight basis, for 1-35%, preferably 1-30%, more preferably 1-25%, and even more preferably 5-20%, of the materials plus water fed to the extruder.
In all of the embodiments listed herein, the presence of a plasticiser serves to give resiliency to the extrudate, which is particularly useful in processing of the extrudate.
Optionally, 0-25% of the materials fed to the extruder on a dry weight basis of a plasticiser, such as glycerol, a sugar or a humectant, may be utilised. Preferably 3-10%, and more preferably 5% of a plasticiser by dry weight of materials fed to the extruder may be utilised, depending on the requirements of the product.
Advantageously, in one embodiment currently being used the inorganic material is present at about 65% by weight, the polysaccharide is present at about 10% by weight and the binder is present at about 20% by weight, of the dry materials fed to the extruder. Water is fed to the extruder, the amount depending on the product characteristics required.
In alternative embodiments of the inventive concept, the formulation comprises inorganic material within the range of 65-80%, polysaccharide material within the range of 8-15% and binder material within the range of 9-20% on a dry weight basis of the materials fed to the extruder.
Suitably the barrel of the extruder has a temperature profile ranging from the feed port, or first section, temperature of less than 65°C, a second section having a temperature of 65°C, a third section having a temperature of 85°C, and a die end, or fourth section, having a temperature of 115°C. The temperature of the extrudate at the die is suitably therefore in excess of 100°C. Extrudate temperatures at the die may, however, range from 50°C to 200°C. Naturally the temperature at the die will depend on the plastics or inorganic material fed to the extruder, the melting point thereof, and the physical requirements of the produced filtration material.
The operating pressure of, as well as the torque and current drawn by, the extruder depends on the material and the formulation of the material running therethrough, the screw speed, the screw configuration, the amount of water in the mixture within the barrel, the feed rate and the die size, for example. The exact operating conditions will therefore be dependent on the material formulation, the extruder configuration and the characteristics of the product required upon extrusion. These can be readily determined by the skilled man without the exercise of inventive ingenuity.
The purpose of introducing water to the extruder is to produce the foamed structure of the extrudate. In the extruder the materials fed thereto are subjected to conditions of heat, shear and pressure such that immediately upon emergence from the exit die of the extruder, the water, or at least a portion thereof, vaporises into steam, thereby creating cells within the extrudate and a consequent swelling of the extrudate. The water may be injected into the extruder through ports in the extruder barrel and/or be fed to the extruder via the feed hopper thereof.
The cellular structure produced by the vaporisation of water at emergence from the exit die of the extruder preferably provides a porous structure for the passage of air and/or smoke. The cellular structure may comprise a proportion of closed cells and a proportion of cells which are inter-connected or open, provided that there is sufficient inter-connection of cells along the length of the extrudate to provide an acceptable pressure drop along a cut portion of the extrudate. The pressure drop can be measured, for example, when a cut portion of the extrudate is placed in a pressure drop testing machine. Pressure drop measurement is an indication of the resistance to air as air is drawn along the length of a cut portion of extrudate.
Preferably the filtration material is extruded as a rod of filtration material, for example, by extrusion to atmospheric pressure through a circular die. For filtration material for use as tobacco smoke filter material this is particularly advantageous, as the arrangement approximates conventional filter rod appearance. The size and characteristics of the rod can also be controlled. Alternatively, the extrudate may take the form of a sheet which may then be cut into shreds and fed through a chimney to the garniture of a cigarette making machine, for example. In a further alternative, the extrudate may be extruded under vacuum into a tubular mould.
The present invention provides a tobacco smoke filter element comprising a rod of extruded filtration material, the rod of filtration material being degradable and being produced in accordance with the method hereof.
On an experimental scale extruder, a Clextral BC21, for example, the die diameter may be from about 2.5 - 10mm. The expanded extrudate issuing from the die may then be sized and shaped to a conventional or required rod diameter. The preferred die size for production purposes may readily be determined upon scaling up of the experimental design to full size.
The composition of the extruded filtration material will be similar to the composition of the materials fed to the extruder because of the closed system of operation. The final product composition will depend on the moisture conditions under which measurement of the product is carried out.
The moisture content of the extrudate exit the die is typically within the range of about 5% to about 35%. The density of the final product after extrusion may be within the range 323mg/cc - 1391mg/cc. Advantageously, the density of the final product is within the range of 100mg/cc - 400mg/cc. Rods of filtration material can be produced according to the inventive method, with densities which are similar to conventional filter rod densities. Naturally, the density of the final product is dependent on the original formulation fed to the extruder, the operating conditions of the extruder and the method by which the extrudate is handled after extrusion.
Extruded rods of filtration material according to the present invention, when wrapped in a wrapper, may be laser ventilated to vary the delivery of tobacco smoke when the rod is attached to a rod of smoking material. The surface of the extruded rod is suitably perforated by the laser treatment. Porous plugwrap may also be used.
It has been observed that the filtration efficiency of extruded filtration material can be substantially constant over a pressure drop range of 30-120mm W.G. per 20mm length of rod. This feature is surprising and is not seen in conventional rods of filtration material.
It has also been observed that cut rods of extruded filtration material, when exposed to the natural environment, rapidly begin to disintegrate in the weathering tester within the equivalent of what would be 24 hours of exposure to the natural environment. This feature is not exhibited by conventional cellulose acetate filter rods.
Rods according to the present invention also exhibit a rod pressure drop within the range of 100mm WG - 7000mm WG for a 100mm length. This pressure drop range is considerably wider than that which is obtainable from conventional cellulose acetate filter rods. A large pressure drop range can be advantageous in terms of providing a large scope for reduction, for example, in the pressure drop range consequent of further processing techniques of the extruded rod downstream of the die.
The pressure drop measurement taken on most of the samples described herein is the pressure drop of the samples without downstream processing exit the die, other than collection by hand in a tray as long rods.
Rods extruded according to the present invention have been found to exhibit a firmness which may be at least about 10% greater than the firmness of rods made of conventional cellulose acetate tow. Applicant has found that it is, however, possible to achieve firmness values which are closer to the firmness values of conventional cellulose acetate filter rods by varying the formulation fed to the extruder. Applicant currently believes that adjustment of the extruder operating conditions gives a lesser effect on firmness than does variation in the formulation.
Extruded rod may also comprise a photodegradable substance which promotes degradation in sunlight.
In order that the present invention may be readily carried into effect reference will now be made to the accompanying diagrammatic drawings, wherein:

Figure 1 shows apparatus for carrying out the method of the invention.

Examples illustrating the present invention were carried out as described below.
As shown in Figure 1, each component may be fed from supply bins 1, 2, 3 to a blending bin 4. The blended components were fed via a K-tron feeder 5 to a Clextral BC21 extruder 6 having a barrel 7 comprising four 100mm barrel sections and a length to diameter ratio of 16:1. The feed port, or first section, of the extruder barrel had been modified and it was not possible to control the temperature of that particular section of the extruder barrel. Water was injected via a pump 8 from a supply source 9 into the barrel section immediately downstream of the feed port. The extruded product 10 was collected by hand immediately exit the extruder die 11 and collected in a long tray.
A plasticiser, sugar or humectant may be added to the extruder barrel 7 via injection line 12 from supply source 13.
After air drying, all the samples were cut in the laboratory to a standard 70mm or 100mm length, weighed and circumference tested using a Borgwaldt laser circumference gauge. Pressure drop was tested on a BAT servo mechanical pressure drop tester. Firmness was also determined by using the standard Borgwaldt filter firmness tester. It was found that, for extrudate which had physical dimensions greater than the largest dimensions capable of being measured in conventional testing machines, it was difficult to determine accurate measurements therefor.

EXAMPLE 1

A series of runs were carried out with inorganic fillers using a Baker Perkins MPF 50 extruder. The barrel temperature along the five sections leading towards the die end section were 50°C, 65°C, 75°C, 85°C and 95°C, respectively.

Each blend used the basic formulation, on an approximate dry weight basis, of 65% inorganic filler, 10% starch, 20% binder consisting of 12% hydroxypropylcellulose and 8% carboxymethylcellulose, and 5% glycerol. Water was further supplied to the extruder barrel. In some runs the inorganic filler comprised a mixture of materials. Details of the inorganic fillers and the physical characteristics of the extruded products are given in Table 1 below.

TABLE 1

Inorganic Filler (% dry weight basis)	Filter Characteristics						Screw Speed (rpm)
	Length (mm)	Weight (mg)	Circumference (mm)	Pressure Drop (mm W.G.)	Pressure Drop of 100mm Length of Filter Rod (mm W.G.)	Die Size (mm)
65% Aluminium hydroxide	70.45	1826	20.6	195	277	4.0	225
32.5% Aluminium hydroxide	70.2	994	23.48	88	125	4.0	225
32.5% Aluminium oxide
49% Aluminium hydroxide	70.45	1493	24.3	126	179	4.5	225
16% Aluminium oxide
Metaspheres 50	99.7	2730	24.18	579	581	6.5	225
Garolite	99.9	2460	24.29	309	309	6.5	225
Verniculite	99.9	3410	24.91	194	194	6.5	230
Trihyde	101.8	6400	23.83	NM		9.0	270

EXAMPLE 2

A further series of runs was carried out on the same extruder and under the same barrel conditions as Example 1, using chalk and carbon as detailed below:

Material	Weight (% dry weight basis)
	Run A	Run B	Run C	Run D
Chalk	-	-	80	71
Carbon	65	70	-	-
Starch	10	8	-	15
Hydroxypropyl-cellulose	12	12	9	9
Carboxymethyl-cellulose	8	5	6	-
Glycerol	5	5	5	5

Water was further fed to the extruder barrel. The physical characteristcs of the extruded rod are detailed in Table 2 below.

TABLE 2

Run	Length (mm)	Weight (mg)	Circumference (mm)	Pressure Drop (mm W.G.)	Pressure Drop for 100mm Length of Filter Rod (mm W.G.)	Die Size (mm)	Screw Speed (rpm)
A	70.2	1600	24.51	231	329	-	-
B	69.5	1700	24.24	390	561	-	-
C	71.1	2660	22.48	NM	NM	6.5	225
D	69.6	1450	24.08	NM	NM	5.0	225

It may be noted that the filtration efficiencies for the experimental filters show a different response to increasing pressure drop than the expected filtration efficiencies for the mono cellulose acetate filters of conventional construction. The filtration efficiencies of rods according to the invention remain effectively constant over the pressure drop range of 30-120mm WG. In contrast, conventional filters show an increase in filtration efficiency as pressure drop increases.
The pressure drop and efficiencies of a conventional cellulose acetate filter are directly related to the total surface area of the fibre used in filter construction. The difference in efficiencies of filters according to the invention and conventional cellulose acetate tow filters suggests that there is a different physical structure in filters according to the invention.
The similarity of filtration efficiency of filters according to the invention may be of use to a cigarette designer. For example, for filter rods of 20mm length and having a pressure drop in the range of 20-120mm WG which have an effectively constant filtration efficiency, the filtration efficiency of said filter rods could, perhaps, be varied by increasing or decreasing the length of the filter rod.
Ventilation may also be used to alter the filter pressure drop and smoke deliveries. The invention allows for the production of filter elements having higher pressure drops but lower filtration efficiencies than a conventional cellulose acetate tow filter of the same length. Ventilation of a filter element produced according to the invention will lower the pressure drop but also increase the overall reduction of some of the mainstream smoke deliveries such that the pressure drop and deliveries of a filter element produced according to the invention will equate to those seen with the cellulose acetate filter in a similar cigarette design. However, smoke components that are normally unaffected by filtration (e.g. gases such as carbon monoxide, vapour phase components, etc.) will be reduced by said ventilation.
It is believed that much larger extrudate diameters could be obtained by varying the operative conditions of the extruder. However, extrudate parameters such as diameter which are much larger than conventional diameters are difficult to measure in conventional testing equipment.

Claims

An extruded filtration material comprising inorganic material, a water-soluble polysaccharide expansion medium, a binder and water, wherein the filtration material is degradable, the water soluble or water dispersible components being dissolved or dispersed and the non-water soluble or non-water dispersible components not forming a fused or melted amalgamation under the weather conditions of the natural environment.
A process of making an extruded filtration material according to Claim 1, wherein inorganic material, water-soluble polysaccharide expansion medium, binder and water are mixed together, and extruded through the exit orifice of an extruder die, the inorganic material being selected so that the melting point thereof is above the operating temperature of the extrusion process at any particular operating pressure, wherein the extruded product is cellular and is degradable, the water soluble or water dispersible components being dissolved or dispersed and the non-water soluble or non-water dispersible components not forming a fused or melted amalgamation under the weather conditions of the natural environment.
An extruded filtration material according to Claim 1 or 2, wherein said inorganic material is comprised of one or more of the group consisting of vermiculite, alumina, aluminium hydroxide, carbon, chalk, Metaspheres 50 (Trade Name), aluminosilicates, such as Garolite (Trade Name), and Trihyde (Trade Name).
An extruded filtration material according to Claim 1 or 2, wherein said inorganic filler material comprises 60-85% by weight, said polysaccharide expansion medium comprises 5-20% by weight, said binder comprises 5-25% by weight, and said plasticiser comprises about 5% by weight, of dry materials fed to the extruder.
An extruded filtration material according to Claim 1 or 2, wherein plastisicer in an amount of 3-10% is further supplied to said extruder.
An extruded filtration material according to Claim 4, wherein said inorganic filler material comprises about 65% by weight, said polysaccharide comprises about 10% by weight, said binder is present at about 20% by weight, and the plasticiser is present at about 5% by weight, of the dry materials fed to the extruder.
An extruded filtration material according to Claim 4, wherein said inorganic filler material is within the range of 65-80%, said polysaccharide material is within the range of 8-15%, said binder material is within the range of 9-20% by weight, and said plasticiser is present at about 5% by weight, of the dry materials fed to the extruder.
An extruded filtration material according to any one of Claims 1-7, wherein the binder comprises one or more of the group comprising a cellulosic binder, a pectin or an alginate.
An extruded filtration material according to any one of the preceding claims, wherein said starch is one or more of maize starch, a starch having a higher proportion of amylose than amylopectin, or a chemically modified starch.
An extruded filtration material according to any one of the preceding claims, wherein, the plasticiser is one or more of the group comprising glycerol, a sugar or a humectant.
A smoking article comprising a degradable smoking material enwrapped in a degradable wrapping material and a degradable filter comprising extruded filtration material enwrapped in degradable wrapping paper, said extruded filtration material being according to any one of Claims 1, 4, 5, 6 or 7 or produced according to Claim 2.